Isothermal solubilities of benzene, dichloromethane, n-propyl acetate, and 2-butanone in poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and two different PMMA/PEMA copolymers at 323.15 K are reported. Data were measured in the concentrated-polymer regime using a quartz crystal balance and are represented by a modified Flory-Huggins equation to within experimental error. The model parameters show a trend with copolymer composition.